An image sensor has a limitation of dynamic range and sensitivity. The image sensor sensitivity is determined by the level of light that can be detected. In dim light scene, the image that captured by the image sensor may appear dark and noise. This is known as sensitivity limitation. The image sensor dynamic range is limited by its noise floor and full-well capacity. In many cases, the dynamic range of the image sensor is lower than the dynamic range present in the scene to be captured. As a result, areas with low light intensity appear dark and noise in the captured image, while areas of high light intensity appear saturated. One technique used to overcome these problems is to capture a plurality of images at the same scene and then merge the plurality of captured images into one image. The plurality of images may be captured with same exposure and merged to reduce the noise. This is equivalent to increasing sensitivity of the image sensor. The plurality of images may also be captured with different exposures and merged to increase the dynamic range. This is known as high dynamic range (HDR) imaging.
Since this technique requires multiple input images, the motion problem may be occurred due to moving elements in the scene. It can cause blurring and ghosting artifacts in output image. This is a well known issue.
In HDR imaging, several techniques for solving motion problem in HDR image have been proposed.
Referring to FIG. 1A and FIG. 1B, an example of system and process for generating HDR image, according to U.S. Pat. No. 7,142,723 (Patent Reference 1) is described. An approach is proposed by which a system and process for generating HDR image involves first designating a reference image; each of the non-reference images is then registered with the reference image; the registration procedure generates a flow field for each of the non-reference images, involved computing a per-pixel optical flow field; the generated flow fields are then used to warp each of non-reference image; the warped images are then combined with the reference image to create a radiance map representing the HDR image. With this approach, the input non-reference images are warped, before combining/merging, to address the motion problem.
[Patent Reference 1] US patent, “System and process for generating high dynamic range images from multiple exposures of a moving scene”, U.S. Pat. No. 7,142,723, 28 Nov. 2006.
Patent Prior Art